How adsorption vs biodegradation sustains the treatability of odorous acetal/terpene in bioactive activated carbon filters

Biological activated carbon (BAC) filtration integrates adsorption and biodegradation to control trace odorants in drinking water, yet sustaining high efficiency in long-aged BAC systems across seasons remains challenging. Here we disentangle the sensitivity of each pathway to operational and environmental drivers using odorous acetals and terpene as key probes. Neither aged BAC adsorption alone (40–60 % removal) nor sand filter biodegradation (70–80 % removal) sustained > 90 % removal at 20 °C. Adsorption correlated primarily with odorant hydrophobicity/molecular weight and empty bed contact time (EBCT), whereas biodegradation was dominated by temperature (5–20 °C) and largely unresponsive to EBCT or backwash frequency, especially in winter. UV₂₅₄ absorbance tracked odorant removal but required temperature correction for higher accuracy. Even with optimized operation, cold-season performance (5–12 °C) often fell short, indicating the need for staged BAC replacement and/or powdered activated carbon dosing. Microbial profiling indicated that aged BAC, characterized by higher biomass and greater metabolic potential, may host more functionally focused communities, which could contribute to the more consistent removal of odorants and dissolved organic carbon compared with younger GAC. Our results identify the mechanistic and operational factors sustaining BAC performance, providing actionable guidance for resilient odorant control under variable temperature regimes.